On the last day of the Flynn-Fletcher family road trip, Candace thinks she'll finally have a couple of hours to relax and not worry about busting her brothers. However, Phineas and Ferb decide to build a truck stop diner on top of the RV. Meanwhile, Doofenshmirtz is also on a road trip, but he's using a big rig to transport his boom juice across the Tri-State Area, which could lead to disaster if Perry doesn't stop him.